<template>
  <ul class="list">
    <li class="item" v-for="letter in letters" :key="letter" :ref="letter" @click="handleLetterClick" @touchstart="handleTarchStart" @touchmove="handleTarchMove" @touchend="handleTarchEnd">{{ letter }}</li>
  </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated() {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick(e) {
      this.$emit('change', e.target.innerText)
    },
    handleTarchStart() {
      this.touchStatus = true
    },
    handleTarchMove(e) {
      if (this.touchStatus) {
        if (this.timer) {
          return false
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
          this.timer = null
        }, 8)
      }
    },
    handleTarchEnd() {}
  },
  computed: {
    letters() {
      const letters = []
      for (let key in this.cities) {
        letters.push(key)
      }
      return letters
    }
  }
}
</script>
<style lang="less" scoped>
@import '~styles/varibles.less';
.list {
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: absolute;
  top: 1.58rem;
  right: 0;
  bottom: 0;
  width: 0.4rem;
  .item {
    line-height: 0.4rem;
    text-align: center;
    color: @bgColor;
  }
}
</style>
